Cell signaling via 3′-phosphorylated phosphoinositides has been implicated in a variety of cellular processes, e.g., malignant transformation, growth factor signaling, inflammation, and immunity. See generally Rameh et al., J. Biol. Chem., 274:8347-8350 (1999). Phosphatidylinositol 3-kinase (PI 3-kinase; PI3K) is responsible for generating these phosphorylated signaling products. PI3K originally was identified as a protein associated with viral oncoproteins and growth factor receptor tyrosine kinases that phosphorylate phosphatidylinositol (PI) and its phosphorylated derivatives at the 3′-hydroxyl of the inositol ring. See Panayotou et al., Trends Cell Biol 2:358-60 (1992).
Three classes of the PI 3-kinase (PI3K) are proposed, based on their substrate specificities. Class I PI3Ks phosphorylate phosphatidylinositol (PI), phosphatidylinositol-4-phosphate, and phosphatidylinositol-4,5-biphosphate (PIP2) to produce phosphatidylinositol-3-phosphate (PIP), phosphatidylinositol-3,4-biphosphate, and phosphatidylinositol-3,4,5-triphosphate, respectively. Class II PI3Ks phosphorylate PI and phosphatidylinositol-4-phosphate, and Class III PI3Ks phosphorylate PI.
The initial purification and molecular cloning of PI 3-kinase revealed that it was a heterodimer consisting of p85 and p110 subunits. See Otsu et al., Cell, 65:91-104 (1991); Hiles et al., Cell, 70:419-29 (1992). Since then, four distinct Class I PI3Ks have been identified, designated as PI3K α, β, δ, and γ isomers, each consisting of a distinct 110 kDa catalytic subunit and a regulatory subunit. More specifically, three of the catalytic subunits, i.e., p110α, p110β, and p110δ, each interact with the same regulatory subunit, i.e., p85, whereas p110γ interacts with a distinct p101 regulatory subunit. As described below, the patterns of expression of each of these PI3Ks in human cells and tissues also are distinct.
Identification of the p110δ isoform of PI 3-kinase is described in Chantry et al., J. Biol. Chem., 272:19236-41 (1997). It was observed that the human p110δ isoform is expressed in a tissue-restricted fashion. It is expressed at high levels in lymphocytes and lymphoid tissues, suggesting that the protein might play a role in PI 3-kinase-mediated signaling in the immune system. The p110δ isoform is described in U.S. Pat. Nos. 5,858,753; 5,882,910; and 5,985,589, each of which is incorporated herein by reference. See also Vanhaesebroeck et al., Proc. Natl. Acad. Sci. USA, 94:4330-5 (1997); and WO 97/46688.
Therefore, there is a need for therapeutic agents that inhibit PI3K isomers to treat disorders or diseases that are mediated by PI3K.